#define _CRT_SECURE_NO_WARNINGS 1

#include <stdio.h>



int main() {

    int n, temp;

    scanf("%d", &n);

    temp = n / 10;

    switch (temp)

    {

    case 10:

    case 9:

        printf("A");

        break;

    case 8:

        printf("B");

        break;

    case 7:

        printf("C");

        break;

    case 6:

        printf("D");

        break;

    case 5:

    case 4:

    case 3:

    case 2:

    case 1:

    case 0:

        if (n >= 0)

            printf("E");

        else

            printf("F");

        break;

    default:

        printf("F");

    }

    return 0;

}